A spark plug of this nature is disclosed in DE 101 44 976 A1. In this spark plug, the center electrode and the ground electrode do not project directly into the combustion chamber of the internal combustion engine, but instead into a prechamber that is formed at the forward end of the spark plug and communicates with the combustion chamber of the internal combustion engine through one or more openings. As a result of the openings in the prechamber, an exchange of gas is possible between the prechamber and the combustion chamber. Spark plugs of this type, which are also known as prechamber spark plugs, are used for the ignition of lean fuel/air mixtures in stationary, gas-powered internal combustion engines. A fuel/air mixture is referred to as lean when the ratio, lambda, of the quantity of air actually present in the combustion chamber to the quantity of air stoichiometrically required for complete combustion of the fuel is greater than 1, where lambda values of 1.6 to 1.7 are desired. In the compression stroke of the internal combustion engine, an ignitable mixture is introduced into the prechamber through the openings of the prechamber. In terms of its function, the prechamber is a precombustion chamber. The ignitable gas/air mixture flowing into the prechamber is first ignited in the prechamber by means of an ignition spark produced between the center electrode and the ground electrode of the spark plug. The flame produced in the prechamber is ejected from the prechamber through the openings therein as a result of the pressure of the combustion arising in the prechamber, and ignites the lean fuel/air mixture present outside the prechamber in the combustion chamber of the internal combustion engine.
Stationary, gas-powered internal combustion engines are designed for a very long service life and accordingly are also in use for long time periods. In order to optimize combustion and running performance, as well as to reduce fuel consumption and pollutant emissions, it is desirable to obtain information about the combustion taking place in the combustion chamber and to adjust the engine controller on the basis of this information. In stationary, gas-powered internal combustion engines that have already been in use for a relatively long time, there oftentimes is still no way of acquiring information from the combustion chamber during operation, since no appropriate sensors or channels are provided in the combustion chamber. It is very resource-intensive to retrofit openings or channels terminating in the combustion chamber, so retrofitting is not possible in practical terms.